MANCHESTER— A technician severely burned in a flash fire inside an underground gasoline storage tank last month died Saturday at a Boston hospital, city and state fire investigators said Wednesday.

Donald Scott, 24, of Andrews, S.C., died at Massachusetts General Hospital where he was being treated since the Sept. 9 explosion and flash fire that left him with third-degree burns over 90 percent of his body, fire officials said.

Another technician, Andy A. Snow, 31, also of Andrews, S.C., suffered third-degree burns mostly from the waist down. Snow had since been released from the hospital and is expected to make a full recovery, fire officials said.

Both men worked for Tank Tech Inc. and were part of a crew of five hired to install a new fiberglass storage tank inside the existing 10,000-gallon tank at the Mobil Kwik Stop at 1095 Hanover St.

Snow was able to escape the tank on his own with severe burns. But co-workers had to place a harness on Scott, which they attached to a cable that they used to pull him by hand from the bottom of the tank, a witness said.

John Brewer, who saw the smoke from his Citgo service station across the street and ran to help, said Scott “was melted from head to toe” but still breathing.

Still, Manchester Fire Chief James Burkush on Sept. 10 said “significant questions” remained about safety procedures and practices employed by Tank Tech.

City fire investigators have been investigating the incident with the State Fire Marshal’s Office, deputy city fire marshal Rick Clement said. Once their report is complete, they will present their findings to the Hillsborough County Attorney to determine if criminal charges can be brought.

A spokesman for Tank Tech Inc. claimed the Manchester incident was the first for the Blodgett, Mo.-based company. Tank Tech has been in business since 1985, spokesman Jonathan McNeeley had said.

But the New Hampshire Union Leader learned the state of Kentucky fined Tank Tech $125 for failure to properly control ignition sources prior to inspecting or working on a tank in Hickman, Ky., resulting in an explosion that killed John Robeson on June 10, 2001.